The present invention concerns a method for adjusting the frequency of a piezoelectric crystal resonator by removing material by means of laser beam shots or pulses which are produced in bursts.
The invention also concerns the piezoelectric crystal resonator produced by carrying out this method.
It is known in particular from U.S. Pat. No. 3,766,616 how to adjust the frequency of a piezoelectric crystal resonator, for example a quartz resonator, by removing a metal layer which partially covers the piezoelectric crystal, the removal of material being effected in a point wise manner. The effect of removing material in this way, which can be performed by using laser beam shots, is to increase the frequency of the resonator which is subjected to this treatment. The frequency of the resonator is measured and compared to the desired frequency after each shot, and, if the measured frequency is lower than the desired frequency, a fresh or succeeding shot is fired. The operation is concluded when the measured frequency is equal to the desired frequency.
The degree of accuracy in measuring the frequency is directly linked to the duration of the measurement operation. Each measurement operation is effected with the maximum degree of accuracy, so that this process suffers from the disadvantage of taking up a fairly long period of time to complete the process. This is incompatible with the requirements of manufacturing the resonators on a very large scale.
The aim of the present invention is to improve the method of using laser beams for the purposes of adjusting the frequency of such a resonator, by reducing to a minimum the total amount of time required for adjusting the frequency thereof.